Automatic fruit graders are used to assess and grade whole fresh fruit and other fresh produce into different categories to create lines of fruit of consistent quality, for example of uniform size or colour. Whereas in the past produce tends to have been graded based on external properties such as size, shape, colour and external blemishes, there is now an increasing trend towards including internal qualities of produce, such as ripeness, taste and firmness, among the properties assessed by automatic graders.
The global market in horticultural grader technology is estimated to be currently $1B p.a., and increasing as world fruit production rates continue to rise. Improved grader technologies are required by fruit suppliers to handle increasing pressure coming from three separate angles. These are (i) preferred supplier status to the large supermarket chains, (ii) supplying fruit that can command a price premium and (iii) reduction in costs by minimising downgraded fruit and labour costs. A particularly strong driver for grading technology has been an increase in consumer expectations of fruit quality. Consumers increasingly expect the fruit they buy to be as consistent as manufactured foods. If a particular quality of a fresh product matters to the consumer then it is in the interest of the producer to measure, and thereby control, that quality. Retailers are responding by imposing strict grade standards, which must be met by their suppliers.
Firmness of produce (eg the ‘crunchiness’ of an apple) is an important factor in the consumers' selection of the produce. There are a number of existing automatic fruit graders designed to measure the firmness of individual items of fruit or produce. However, adequate solutions for determining the firmness of a fruit do not presently exist. The problems are difficult to solve since the sensor technologies must be non-destructive to the fruit, able to be integrated into existing systems without significantly reducing the overall throughput of the system, and accurate regardless of the size, presentation and morphological character of the fruit.
There are existing systems for determining the firmness of a fruit, for example the simple acoustic firmness sensor offered by Aweta, and sensors offered by Greefa and Sinclair. However, these existing systems require contact with the fruit. This requirement immediately imposes a number of constraints on the measurement, the most significant being speed but also often a considerable degree of mechanical complexity to overcome that problem. For example, the Sinclair IQ Firmness Tester uses a set of bellows to lower a firmness sensor onto fruit. The Greefa iFD uses a complex mechanical assembly to synchronise sensors with the fruit conveyor. Additionally, these existing systems are not capable of cooperating with systems which involve high speeds of conveying fruit. For example, the Greefa iFD has a maximum throughput of five fruit per second per lane.
There are generally two broad classes of grading device for measuring product firmness; the deformation method and the acoustic method. Both these methods suffer from disadvantages.
The deformation method involves measuring the response at the surface of the fruit to pressure or an impact applied at one location. This method generally requires the system to be in physical contact with the fruit. One disadvantage with the deformation method is that the system takes a measurement from a single point measurement and is therefore vulnerable to soft patches. These vulnerabilities include measuring in a soft patch and underestimating the firmness, missing a soft patch which might represent a fault, or being insensitive to broad variations around the fruit (for example being firmer on the shaded side). This disadvantage may be overcome by taking a number of measurements at different locations around the fruit. However, that approach is time consuming and reduces the throughput of the system even further. A further disadvantage with the deformation method is that such techniques may be relatively insensitive with firm fruit where deformations are small.
A system and method of implementing the deformation method using a single-point firmness measurement which does not require physical contact has been described in U.S. Pat. No. 5,372,030 (to Prussia et al). The system described in Prussia uses a jet of air to depress the surface of a fruit and a laser displacement meter to measure the resulting deformation of the fruit. The device requires large volume of pressurised air which can be commercially prohibitive. In addition, the deformation technique may be less sensitive with firm apples.
The system implementing the acoustic method uses a member to physically tap a fruit to vibrate the fruit and measures the resonant frequency of the vibration to estimate the stiffness of the fruit flesh. One disadvantage with the acoustic method is that both fruit size and shape affect the resonant frequency. Both these parameters must be known along with the resonant frequency before flesh firmness can be inferred. The size and shape of fruit are often measured by the grader and can be readily used to estimate flesh stiffness. Another disadvantage with the acoustic approach is that the sound emitted from the vibrating fruit is very small, and the acoustic pickup must be appropriately shielded from ambient noise. This must generally be done by holding the pickup against the fruit, which can be difficult to achieve in the short time available and with moving fruit. A further disadvantage with the acoustic method is that the physical tapping of the fruit can be difficult to perform, for the same reasons as for the deformation method. The speed of the fruit on the conveyor and the risk of damage to the fruit surface make it difficult to impact the fruit accurately with a physical tapper.
Manual sorting using trained operators is the only alternative means to grade for firmness and surface defects. Although accurate in some circumstances, depending on the product and/or defect, manual grading is notoriously unreliable and only economically viable in countries where suitable labour is inexpensive.
Embodiments of the present invention seek to overcome the disadvantages of the existing systems and to provide an improved system and method for non-destuctively determining a property of an object, or to at least provide the public with a useful choice. An alternative object of the present invention is to provide a valve that is suitable for delivering a short duration burst of fluid, or that at least provides the public with a useful choice.
In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form any part of the common general knowledge in the art.